The present invention relates to polymer composite materials containing carbon nanotubes, particularly to composites containing singled-walled nanotubes, in which the nanotube is solubilized or dispersed in a polymer by contacting the nanotube with a m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene.
Multi-walled carbon nanotubes (MWNTs) were first discovered in 1991 as a result of research on fullerenes. [S. Iijima (1991)]. Several years later single walled carbon nanotubes (SWNTs) were discovered. [S. Iijima and T. Ichihashiy (1993)]. A SWNT can be described as a giant molecule made from a single sheet of graphite wrapped around and joined with itself to form a cylinder whose two ends are each capped with the hemisphere of a fullerene. Multi-walled carbon nanotubes are made up of several of these tubes, where smaller diameter tubes are concentrically contained within larger diameter tubes. SWNTs are known to self-aggregate to form ropes [A. Thess et al. (1996)]. Carbon nanotubes have been found to possess a wide variety of extraordinarily useful properties, encouraging interest, especially within the past few years, in development of the technology required to exploit these properties. (See: Ebbesen (ed.) “Carbon Nanotubes, Preparation and Properties” CRC Press (1996); Saito R. et al. “Physical Properties of Carbon Nanotubes” World Scientific (1998); Dresselhaus et al. “Carbon Nanotubes: Synthesis, Structure, Properties and Applications” (2000) Springer-Verlag.) Their potential for use as composite reinforcements comes from their remarkable mechanical properties. Carbon nanotubes potentially have excellent fiber reinforcement properties in part because of their exceptionally high aspect ratios (the length of the tubes relative to their diameter) which can be as great as or greater than one million. Their theoretical strength has been calculated to be more than one hundred times that of steel, and yet they are only one sixth the density of steel. They have also been found to be much stiffer than other reinforcement materials, such as carbon fibers, but are much less brittle. Their potential to produce materials with a high strength to weight ratio make them ideal reinforcement candidates for incorporation into advanced structural composites for the various applications, particularly in the aerospace industry. These materials have potential application in many consumer products from automobiles to sports equipment.
In addition to extraordinary mechanical properties, carbon nanotubes are predicted to have useful electronic, thermal and magnetic properties. Some of these other properties are capable of being tuned by varying the diameter and/or the chirality of the tubes. [M. S. Dresselhaus, et al. (1996)]
The difficulty in realizing the potential carbon nanotubes have for providing enhanced mechanical strength to polymer based composites has been their inability to homogeneously or uniformly disperse, either in the polymer precursors or in the polymers themselves. Carbon nanotubes, and particularly single walled carbon nanotubes (SWNTs), can be micrometers or even longer in length. While their extremely long length relative to their width means that they should have good fiber properties, it also means that they are not readily soluble in solvents. While there has been some success at dispersing shorter nanotubes in polymers, composites made with these short nanotubes having low aspect ratios have not realized the anticipated increases in the strength of the final composite.
Recently, Curran et al. (1998) reported that MWNTs (500 nm to 1.5 micron in length) were dissolved in a toluene solution using the polymer poly (m phenylenevinylene co-2,5-dioctoxy-p-phenylenevinylene) [abbreviated as co-2,5-dioctyl-PmPV]. They authors indicated that they were able to get the nanotubes to dissolve in organic solvents, such as toluene, because the co-2,5-dioctyl-PmPV polymer wrapped around the nanotube and held it in suspension in the polymer/toluene solution. In part, it was believed that the polymer employed separated ropes of SWNTs. The authors reported mixing nanotube powder and the co-2,5-dioctyl-PmPV polymer in toluene and briefly sonicating the mixture to obtain dissolution. The structure of co-2,5-dioctyl-PmPV is a variation of the more common light-emitting polymer polyphenylenevinylene (PPV). The bonds between the two alternating moieties making up the polymer backbone in co-2,5-dioctyl-PmPV, however leads to dihedral angles in the chain causing the chain to coil, thereby forming a helical structure along the polymer backbone. The diameter of this helix in a vacuum has been calculated to be 2 nm with a pitch of 0.6 nm. The size of the helix, as pointed out by the authors “fits nicely around a nanotube.”
U.S. Pat. No. 6,576,341 and EP patent 094919B1 relate to the use of an organic material, particularly a polymer, to purify nanotube soot by forming a nanotube/polymer composite suspension in a solvent. The composite is then separated from the solvent. Preferred embodiment of the invention the organic material is a polymer. A preferred polymer is poly(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene). Other organic materials said to be useful in the invention are poly(dioctyl fluorene), poly(sulphonic acid), polyacetylene and DNA.
Published PCT application WO/02/16257 (published Feb. 28, 2002) reports polymer wrapped or coated SWNTs. Amphiphilic polymers, such as polymer surfactants, were said to be useful in the invention. Specific polymers said to be useful in the invention were polyvinyl pyrrolidone, polystyrene sulfonate, poly(1-vinyl pyrrolidone-co-vinyl acetate), poly(1-vinyl pyrrolidone-co-acrylic acid), poly(1-vinyl pyrrolidone-co-dimethylaminoethyl methacrylate), polyvinyl sulfate, poly(sodium styrene sulfonic acid-co-maleic acid), dextran, dextran sulfate, bovine serum albumin, poly(methyl methacrylate-co-ethyl acrylate), polyvinyl alcohol, polyethylene glycol, polyallyl amine, and mixtures thereof. SWNTs wrapped or coated with PVP are exemplified. The polymer-wrapped or coated SWNTs are said to be useful in mechanical and structural applications. The polymer-wrapped or coated SWNTs are said to be useful in the preparation of electrically-insulating material having wrapped or coated SWNTs suspended in them. Electrically insulating materials including poly(methyl methacrylate), polystyrene, polypropylene, nylon, polycarbonate, polyolefin, polyethylene, polyester, polyimide, polyamide, epoxy, and phenolic resin are reported to be useful in materials of the invention. SWNTs are reported to be successfully solubilized by wrapping with PVP polymers, polystyrene sulfonate (PSS), poly(1-vinyl pyrrolidone-co-vinyl acetate) (PVPNA), poly(1-vinyl pyrrolidone-co-acrylic acid), poly(1-vinyl pyrrolidone-co-dimethylaminoethyl methacrylate), polyvinyl sulfate, poly(sodium styrene sulfonic acid-co-maleic acid), dextran, dextran sulfate, bovine serum albumin, poly(methyl methacrylate-co-ethyl acrylate), polyvinyl alcohol, polyethylene glycol, and polyallyl amine. The published application provides the following explanation “the examples indicate that the wrapping of the SWNTs by water-soluble polymers is a general phenomenon, driven largely by a thermodynamic drive to eliminate the hydrophobic interface between the tubes and their aqueous medium.” Several US patent applications are related to this PCT published application: US 200020046872, US 20020048632 and US 200020068170 (all filed Aug. 23, 2001). This reference does not however report functionalization of polymers used for solubilizing carbon nanotubes and does not teach or suggest selection of functionalization of the wrapping polymer for compatibility with the electrically insulating materials into which the carbon nanotubes are to be introduced.
U.S. Pat. No. 6,331,265 relates to reinforced polymers containing carbon nanotubes. Carbon nanotubes are reported to be introduced into a polymer, followed by stretching the mixture at or above the melting temperature of the polymer to orient the nanotubes. The patent discusses problems associated with orienting carbon nanotubes in polymers. Specifically disclosed polymers are polyolefins, such as a polyethylene or a polypropylene or blends thereof.
U.S. Pat. No. 6,265,466 relates to a composite having oriented nanotubes to provide electromagnetic shielding. The composite is made by adding nanotubes to a polymer and imparting a shearing force to the polymer and nanotubes to orient the nanotubes. Polymeric material said to be useful in the invention include thermoplastics, thermosets, and elastomers and more specifically polyethylene, polypropylene, polyvinyl chloride, styrenics, polyurethanes, polyimides, polycarbonate, polyethylene terephthalate, acrylics, phenolics, unsaturated polyesters, as well as the natural polymers cellulose, gelatin, chitin, polypeptides, polysaccharides, or other polymeric materials of plant, animal, or microbial origin.
U.S. Pat. No. 6,746,627 relates to an electrically conductive composite comprising a polyvinylidene fluoride polymer or copolymer and carbon nanotubes. The composites are prepared by mixing or dispersing carbon nanotubes in polymer emulsion using an energy source (e.g., a blender) followed by removal of the liquid to obtain the composite.